[SAI_Peregrinus]

Bookmarks have a really, really bad interface compared to tab trees.

Bookmarks are flat by default. You can make folders, but that takes manually opening the bookmarks manager and placing newly created bookmarks into the appropriate folder. Folders also waste space in the tree; one bookmark can't directly be the parent of another. The web doesn't have folders, it has links.

Bookmarks don't preserve structural context the way tab trees do. For example when using an API documentation site I'll open the site in a window, and from there open classes I need info on in tabs. Methods or related classes go in sub-tabs. I eventually end up with tabs for all the bits of the API I need to reference AND THE STRUCTURE!

Bookmarks are also hidden behind a menu, and are slow to access. Tabs can simply be suspended to save resources, and their trees collapsed.

Etc, etc. Bookmarks have horrible UX compared to tab trees.